This invention relates to a dragline rigging system, and more specifically to a dump line for a dragline rigging.
Conventional dragline riggings include a pair of drag lines connectable to drag hitches on the cheeks of a dragline bucket for dragging the bucket through material to be excavated, a pair of hoist lines connectable to trunnions on side walls of the bucket for hoisting the bucket, and a dump rope for tipping the bucket. Generally, the hoist lines include a pair of lower hoist chains, a spreader bar for holding the lower hoist chains away from the bucket side walls during hoisting, and a pair of upper hoist chains for connecting the spreader bar to a pair of hoist ropes by way of a tri-link. To allow for tipping of the bucket, the dump rope is arranged to extend over a pulley linked to the hoist lines, and is connected at one end to the front of the bucket and at the other end to the drag lines.
The useful life of the dump rope in conventional rigging systems tends to be relatively short, typically only several weeks. The main reason for this is that, for practical reasons, the diameter of the pulley is limited and this limits the diameter of the dump rope which can be used with the pulley. If the diameter of the dump rope is too large, bending stresses in the rope as it passes over the pulley in use cause the rope to overstress and fail within a relatively short time. On the other hand, if the diameter of the rope is decreased to prevent premature failure of the rope due to bending stresses, the fatigue strength of the rope is generally insufficient to receive the dump-line loads for more than a few weeks.
Each time a dump rope on a dragline rigging is replaced, the down-time has a considerable effect on the productivity of the dragline. Accordingly, various proposals have been made to increase the durability of the ropes by for instance coating the ropes with a polyurethane coating or using special lubricants. However, none of these proposals have proved to substantially increase the useful life of a dump rope.
It is an object of the present invention to provide an alternative dump line for a dragline rigging which has a substantially increased useful life when compared with conventional dump ropes for dragline riggings.
According to the invention there is provided a dragline rigging system including:
a pair of drag lines connected or connectable to drag connection points on a dragline bucket for dragging the bucket through material to be excavated;
a pair of hoist lines connected or connectable to hoist connection points located at or near the rear of the dragline bucket for hoisting the bucket with excavated material during excavation; and
a dump line which is arranged to extend from the drag lines over a pulley linked to the hoist lines and to a dump connection point located at or near the front of the dragline bucket for lowering the front of the bucket during dumping of excavated material, at least a substantial portion of the dump line comprising a composite belt which includes an inner material for receiving loads and an outer protective cover for resisting wear.
In a preferred embodiment of the invention, the inner material comprises a woven fabric or wire ropes, and the outer protective cover comprises a synthetic or natural rubber or a wear-resistant grade of polyurethane.
The composite belt may include a smooth or substantially smooth surface which is arranged to engage with a corresponding surface on a pulley.
Alternatively, the belt may include a plurality of teeth for engaging corresponding teeth on a pulley, or a series of centrally located projections which are arranged to run within a central slot in a pulley. In a particularly preferred embodiment, the pulley is formed from an engineering plastics such as NYLON, a fibreglass composite, or a combination of an engineering plastics and a fibreglass composite.
The invention also extends to a composite belt for a dump line on a dragline rigging system including a pair of drag lines and a pair of hoist lines, the composite belt having an inner material for receiving loads, an outer protective cover for resisting wear, a formation for attaching the belt to the drag lines, a formation for attaching the belt to a dump connection point located at or near the front of a dragline bucket, and an engaging surface for engaging a pulley linked to the hoist lines.